Lithography is the process of writing a circuit design (or geometry) onto a mask. Related art lithography (or write) equipment, writes the geometry onto a plate by exposing a resist with a laser or a charged beam. This exposure changes the molecular composition of the resist, and during a developing process the exposed resist is removed. In some alternative applications, a negative resist is used. In this case, the non-exposed resist is removed during a developing process.
Photomasks (or masks) are relatively high precision plates containing microscopic images of electronic circuits. Photomasks are made from substrates, such as, for example, relatively flat pieces of, for example, quartz or glass with a layer of chrome on one side. Etched in the chrome is a portion of an electronic circuit design. This circuit pattern on the mask is also referred to as a geometry.
Masks are used in related art methods of wafer fabrication and wafer writer systems, to create, for example, integrated circuits (ICs). ICs are used in products, such as, computers, calculators, cars, cameras, stereos, etc. Masks are also used in producing flat panel displays, thin film heads, PC boards, etc.
In a related art method of manufacturing a mask, a circuit pattern is designed (e.g., by a customer), and the designed pattern information is digitized. The digitized pattern design data containing a design for a mask is then provided to a mask manufacturer. One or more layers of the pattern design data form a single mask, and an IC circuit comprises a plurality of layers (e.g., about 40 for relatively high-end designs), however, each layer of the resultant circuit may be formed by a single mask in a wafer manufacturing process. The digitized pattern design data may be provided to the mask manufacturer on a disk, magnetic tape, via Internet, dedicated lines, etc.
The mask manufacturer formats the received data for the write or pattern generation system. The formatting may include, for example, fracturing the data, sizing the data, rotating the data, adding fiducials and internal reference marks, and creating instructions for the placement of all the different patterns on the mask, also known as a “jobdeck.” The jobdeck contains instructions describing how to print the mask, what pattern files to use, what layers in the pattern files to use and what transformations to apply. Jobdecks and information included therein are well-known in the art, and therefore, a detailed discussion will be omitted for the sake of brevity.
In one related art method of fracturing data, pattern design data is translated into a language the write system understands. For example, if the pattern to be written is a polygon shape, but related art write systems understand rectangles and trapezoids, the design pattern data is fractured into rectangles and trapezoid shapes. The jobdeck with the fractured data is stored on a computer readable medium (e.g., a disk, flash memory, compact-disc, etc.) and sent to the write system. The write system then prints the pattern on the substrate using the formatted design pattern.
During printing, additional pattern processing takes place. For example, geometries may be spatially re-organized to match a writing sequence of a writing tool and rendered into pixels to be imaged by the exposure system.
A writer system has relatively little understanding of the pattern to be printed on the substrate. The writer system is fed with relatively large amounts of primitive geometries to be printed, but the primitive geometries do not form a meaningful whole until the mask is completely written. Some areas of the design, however, may be more critical than others. For example, some portions of the design may have a higher mask error enhancement factor (MEEF), may have a greater impact on the critical dimension (CD) of the printed pattern and/or may be more critical for proper area coverage. Information regarding the relative significance of these aspects of the design may be available in processing steps upstream from the writing system; however, in related art pattern generation systems, this information is unused and lost as the design pattern data propagates down stream and eventually is printed on a substrate.
Related art lithography writer systems have a finite resolution. Because corners of the pattern represent an infinite spatial frequency, the replication of the design pattern data onto the substrate is compromised, for example, corners of the pattern become rounded. By adding or subtracting energy in the corners, or in the close proximity to the corners, sharpness may be improved. However, a writer system is supplied with fractured data (primitive geometries) that are part of more complex shape, and the relation between the primitive geometries and the shapes they form when combined is lost during fracturing, and thus, is not conveyed to the writer system.
In addition, in a raster based system, no information regarding corners of the pattern is available because the image representation is an approximation of vector data. With just the raster image as input, corners of the pattern must be recreated using advanced search algorithms. However, in this case, the search is relatively difficult and complex because the raster image has a lower resolution than the vector data.